Abrasion-resistant vulcanizates

ABSTRACT

Abrasion-resistant vulcanizates are provided comprising a rubber, finely-divided reinforcing siliceous pigment, a compound having a plurality of reactive amino groups, an aromatic hydroxy compound, and a methylene donor. Rubber additives are provided comprising a finely-divided siliceous pigment having adsorbed thereon at least one but not more than two of the group selected from a compound having a plurality of reactive amino groups, an aromatic hydroxy compound, and a methylene donor.

United States Patent [191 Doran, Jr. et al.

[ June 28, 1974 ABRASION-RESISTANT VULCANIZATES Inventors: Thomas J.Doran, Jr., Norton;

Henry C. Stevens, Akron, both of Ohio Assignee: PPG Industries, Inc.,Pittsburgh, Pa.

Filed: Dec. 6, 1971 Appl. No.: 205,295

US. Cl 260/3, 152/330, 260/3,

260/38, 260/4l.5 A, 260/845, 260/846 Int. Cl C08d 9/10, C08g 37/16 Fieldof Search 260/3, 845, 846, 38

References Cited UNITED STATES PATENTS 8/1968 Ney 260/845 2/1972Endter.... 260/3 8/l972 Klotzer... 260/846 9/1972 Klotzer 260/846 OTHERPUBLICATIONS Chem. & Eng. News, 4/22/68, pp. 40-41.

Primary ExaminerJohn C. Bleutge Attorney, Agent, or Firm-lrwin M. Stein[5 7] ABSTRACT Abrasion-resistant vulcanizates are provided compris- 8Claims, N0 Drawings ABRASION-RESISTANT VULCANIZATES This inventionrelates to the improved abrasionresistant vulcanizates suitable for useas tire treads and to rubber additives for incorporation in saidvulcanizates. More particularly, this invention relates to vulcanizatesof a rubber, a finely-divided siliceous pigment, a compound having aplurality of reactive amino groups, an aromatic hydroxy compound, and amethylene donor; and a rubber additive comprising a finelydividedsiliceous pigment having adsorbed thereon at least one but not more thantwo of the group selected from a compound having a plurality aminogroups, an aromatic hydroxy compound, and a methylene donor butpreferably the amino and hydroxy compounds are not adsorbed on thepigment as some reaction may occur before the methylene donor is added.

The siliceous pigment (alternatively referred to herein as the silicapigment) includes both pyrogenic and precipitated silica of the typeheretofore employed for rubber compounding. The siliceous pigment,however, is preferably of the type obtained by the precipitation from asoluble silicate, for example, silica produced according to the methoddescribed in US. Pat. No. 2,940,830. These pigments have an SiO contentof at least 50 percent and usually greater than 80 percent by weight onan anhydrous basis. The siliceous pigment should have an ultimateparticle size in a range of 50 to 10,000 angstroms, preferably between50 and 400 and, more preferably, between 100 and 300 angstroms. The BETsurface area of the pigment as measured using nitrogen gas is preferablyin the range of to 600, usually to 300 square meters per gram. The BETmethod of measuring surface area is described in the Journal of theAmerican Chemical Society, Vol. 60, page 304 (1930). A typicalcommercial form of such reinforcing siliceous pigment is manufacturedand sold by PPG Industries, lnc., under the designation Hi-Sil 233.

The rubber can be of any of the commonly employed types such as, forexample, natural, or synthetic rubbers such as silicone, chloroprene,polybutadiene, polyisoprene, EPDM, butadiene, and styrene-butadienerubbers. For use in tire treads, however, the rubber is preferably ofthe conventional type such as styrenebutadiene rubber, butadiene rubber,EPDM, and most preferably natural rubber.

The compound having a plurality of reactive amino groups should have atleast two and preferably five or more of said groups. They can be bothprimary and/or secondary amino groups but at least one of said groupsshould be a primary amino group. Suitable compounds include, forexample, polyamines, polyimines, amino acids, poly proteins, aminosugars, deacetylated chitin, gelatin, and similar compounds, to includecompounds containing aliphatic, aromatic and both aromatic and aliphaticmoieties. The preferred amino compounds are polyethylenimines which arehighly branched polyamines composed of units which have two carbons pernitrogen and these units are randomly distributed in the approximateratios of one primary amino nitrogen/two secondary amino nitrogens andone tertiary amino nitrogen. The aforesaid amino distribution gives riseto what is believed to be a molecule with many branched segments and thetertiary amino nitrogens being the mine; alkylether-substitutcd imines,such as methoxypropylenimine, l,B-dibutoxypropylcnimine, l-methyll,4-diethoxybutylcnimine-2,3,; l-ethylene gem diether (propylenimine);unsaturated polyalkylene amines such as polyvinylaminc, andpolyallylamine; polycycloalkylenimines such as prepared by the reductionof polyvinyl pyridine; polyarylenamines, such as polyphenyleneamine andpolymethylenepolyphenylamine; polyglycolamines, and copolymers preparedfrom ethylene oxide and ethylenimine or ethylene sulfide andethylenimine; and heterocyclic polyamines such as derived from 2-vinylpyridine, 2-methyl, 5-vinyl pyridine, and copolymers of 2-vinyl and 2-methyl, 5-vinyl pyridines. Exemplary of the preferred amines are thoseillustrated by US. Pat. Nos. 3,335,116 and 3,579,488 (which areincorporated by reference in their entirety) and polyoxyalkyleniminessuch as polyoxypropylendiimine.

Exemplary of suitable aromatic hydroxy compounds which can be employedinclude resorcinol, catechol, phloroglucinol, phenol, and low molecularweight resorcinol-formaldehyde resins having free phenolic hydroxyls.The preferred compounds are those having two hydroxyl groups which aremeta to each other as the methylene donor reacts more easily with suchhydroxy compounds.

The methylene donor is a compound which reacts like formaldehyde uponheating and includes, for example, hexamethylenetetramine, hexamethoxymethyl melamine, paraformaldehyde, Cohedur A produced by FarbenfabrikenBayer and Oxazolidine A, E and T, each manufactured by CommercialSolvent Corporation.

Other conventional ingredients can be incorporated into the rubbercompound depending upon its use such as, for example, fibers to includefiberglass, nylon, brass-coated wire, a coloring or reinforcing amountof carbon black as well as the conventional accelerators (e.g.,diphenylguanidine) activators (e.g., zinc oxides), curatives (e.g.,sulfur), and the like.

The quantities of ingredients will depend upon the uses and particularcompounds employed and is not a part of the invention but generally frombetween about 5 and about parts by weight siliceous pigment per 100parts of rubber polymer (hereinafter referred to as p.h.r.) is employedand the aromatic hydroxy compound, methylene donor and amino compoundwill each individually be present within the range from between O.l and15 parts p.h.r. and preferably between about 0.5 and about 8 partsp.h.r.

The compounds can be prepared in the conventional manner as illustratedby the following examples but preferably the methylene donor andcuratives are added on the rubber mill to a homogeneous mixture of theother ingredients. Conventional Banbury mixers and rubber mills can beemployed.

If desired, one or two of the coupling agent components can be mixedwith the siliceous pigment prior to incorporating the pigment into therubber batch but preferably the amino and hydroxy compound are not bothadsorbed on the silica. The adsorption can be accomplished such as bymixing at a temperature between about andabout 80 C. in a solvent suchas water, benzene, xylene, or other suitable nonreactive solvent for thecoupling agent for between about 1 and for about minutes at atemperature of between 300 and 320 F. Stress-strain sheets and Picoabrasion buttons were prepared from these compounds and physicalproperties were measured on these samples. The

120 minutes until the coupling agent component(s is 5 data is tabulatedin Table 2 adsorbed on the siliceous pigment. ln manner, thE Theompounds in Examples 5 through were prepl agents are Pften ly $60115,hlgh pared by adding the rubber to a Brabender maintained l dlfficultyfilsperslble mammals can be more at a temperature of about 165 C. andthereafter adding p y Incorporated the rubber batch and any withmastication:polyethylenimine 1 minute after the dency of the rubber tobecome overheated or scorched, l0 rubber; resorcinol, 1 minute th ft andHis 233 Obvlated or {nmlmlzedand phenyl-beta-napthylamine 1 minutethereafter; and h followlng examples W111 f to Illustrate the themixture masticated for an additional 3 minutes to Ventlon and p fembodlmems-r p obtain a homogeneous mixture. With the compounds in p Q F531d mp and elsewher? which zinc oxide was incorporated in theBrabender, Speclficatlon are y Weight (unless otherwlse the zinc oxidewas added to the rubber after 3 minutes cared). of mastication and the'l-li-Sil added 1 minute thereafter. The homogeneous mixture was thenput on an open EXAMPLE I rubber mill at a temperature of about 100 F.wherein I a 1 li roundbottomed 3 k d fl k the hexarnethylenetetraminewas added followed by equipped with a mechanical stirrer was placed 100t other Ingredients marked by the asterisk.

TABLE 1 Compound Compound (Parts by Weight) IngredientsStyrene-butadiene I00 100 100 I00 rubber Natural rubber 100 100 100 I00100 I00 Hi-Sil 233' 60 60 60 60 60 60 60 60 60 60 Composition of 63 6363 63 Example I Phenylbeta-napthylamine l l l l l l l l l Resorcinol 2.52.5 2.5 2.5 L1 2.2 3.3 3.3 2.2 PEI-I2 0.9 0.9 0.9 1.8 0.9Hexamethylenetetramine l.6 l.4* 2.8* 4.2" 42* 28* EesotropiwParaformaldehyde 3.3 Oxazolidine T 3.2 4.8 Sulfur* 2.5 2.5 2.5 2.5 2.52.5 2.5 Santocure N: l l l l l l Diphenylguanidine* l l l l l l Zincoxide 4* 4* 4* 4* 4 4 4 4 4* 4 2.2'-Dithiobis(benzothiazole)75 .75 .75.75 Di-ortho-tolylguanidine* 1.5 1.5 1.5 1.5

Tetramethylthiuram .25 .25 .25 .25

Precipitated silica manufactured by PPG Industries. lnc.--'Polyethylenimine l200 MW.. manufactured by Dow Chemical Co."Equimolar addition compound of resorcinol and hexamethylenetetramine.Methylene donor manufactured by Commercial Solvents Corporation.

"fi-sislehsuiis zsthezglefis!isvsr murmured by Monsanto amps");

grams of precipitated silica (Hi-Sil 233 manufactured by PPG Industries,Inc.) and 600 milliliters of benzene. 55

A Dean-Stark azeotropic distillation trap was mounted on the flask andthe mixture heated until about 3 milliliters of water was distilled off.The mixture was allowed to cool to room temperature and then a solutionof 5 grams of polyethylenimine (Dow Chemical PEI 12,

1,200 average molecular weight) in 100 milliliters of benzene was addeddropwise with stirring. The mixture was stirred for 1 hour and thetreated pigment was isolated by filtration and dried to constant weightby heating in a vacuum oven at a pressure of 20-50 millimeters mercuryand a temperature of 5065 C. for 24 hours.

The following rubber compounds were compared by' mixing the ingredientsshown in Table 1 (other than the 1 7 ingredients marked by an asteriskwhich were added to EPiWlZQEElPPF. ei laasarvk e mi l. anPs y The rubbercompounds in Table l were then subjected to various physical tests andthe results are re- P s s... sthsfqllsw ns Table 21 TABLE 2-Continued90% I Cure 300% Plco 300F. Modulus Tensile Elongation; Hardness Abrasion(p (PS1) (psi) 1 7 emma (Ing s 5 (Min.)

s 13 2810 4470 440 87 12s 9 17' 2560 4630 480 35 H6 28 1150 3070 530 7881 Tested according to ASTM D-4l2-49 T. Tested according to ASTM D-3 l4.

ft ser vs 4.5T Mil-2. 2. 1: .v V

rubber, the natural rubber compounds are unusually effective.

The procedure employed for compounds 1 through 4 in which the silica istreated with the polyimine is preferred for the reason that a difficultydispersible mass can result when all of the ingredients are reactedsimultaneously before a homogeneous mixture can be obtained. Thus, it ispreferred that the polyimine be reacted with the silica prior toincorporation into the rubber batch or that the phenolic compound beblended with the silica or with the polyamine treated silica. Of theaforesaid ingredients, the methylene donor is preferably added last onthe rubber mill.

While there are above described a number of specific embodiments of thepresent invention, it is obviously possible to produce other embodimentsin various equivalent modifications thereof without departing from thespirit of the invention.

Having set forth the general nature and specific embodiments of thepresent invention, what is claimed is particularly pointed out in theappended claims.

We claim:

1. An abrasion-resistant vulcanizate of siliceous pigment reinforcedrubber selected from natural rubber, silicone rubber, chloroprenerubber, polybutadiene rubber, polyisoprene rubber, EPDM rubber orstyrenebutadiene rubber, from about 0.1 to about 15 parts, per

parts by weight of the rubber, each of (a) polyamine or polyiminecompound selected from polymers of ethylenimine, propylenimine,1,2-butylenimine, 2,3- butylenimine, Z-methyl propyleniminealkyloxyalkylenimine, unsaturated polyalkylene amines and cycloalkylenimines, said polymers having a plurality of reactive aminogroups at least one of which reactive amino groups is a primary aminogroup, (b) aromatic hydroxy compound selected from resorcinol, catechol,phloroglucinol, phenol, and low molecular weight resorcinol-formaldehyderesins having free phenolic hydroxyls, and (c) a methylene donorcompound selected from hexamethylenetetramine, hexamethoxymethylmelamine and paraformaldehyde.

2. The vulcanizate of claim ll wherein the siliceous pigment isprecipitated silica.

3. The vulcanizate of claim 1 wherein the compound having reactive aminogroups is polyethylenimine.

4. The vulcanizate of claim l wherein the compound containing reactiveamino groups, the methylene donor, and aromatic hydroxy compound areindividually present in an amount from between about 1 and about 8 partsper 100 parts by weight of the rubber.

5. The vulcanizate of claim 1 wherein the siliceous pigment is presentin amounts of between about 5 and about 100 parts per 100 parts byweight of rubber and the aromatic hydroxy compound, methylene donorcompound and compound containing reactive amino groups are eachindividually present between about 0.5 and about 8 parts per 100 partsby weight of rubber.

6. An abrasion-resistant vulcanizate of rubber selected fromstyrene-butadiene rubber, butadiene rubber, EPDM rubber, and naturalrubber, precipitated siliceous pigment, polyethylenimine having at leastfive reactive amino groups, at least one of which amino groups is aprimary amino group, resorcinol, and hexamethylenetetramine, wherein thesiliceous pigment is present in an amount between about 5 to about 100parts and the polyethylene imine, resorcinol and hexamethylenetetramineare each individually present in an amount between about 0.5 and about 8parts per hundred parts by weight of rubber.

7. The vulcanizate of claim 6 wherein the rubber is natural rubber.

8. The vulcanizate of claim 3 wherein the polyethylenimine has at leastfive reactive amino gro ups.

2. The vulcanizate of claim 1 wherein the siliceous pigment is precipitated silica.
 3. The vulcanizate of claim 1 wherein the compound having reactive amino groups is polyethylenimine.
 4. The vulcanizate of claim 1 wherein the compound containing reactive amino groups, the methylene donor, and aromatic hydroxy compound are individually present in an amount from between about 1 and about 8 parts per 100 parts by weight of the rubber.
 5. The vulcanizate of claim 1 wherein the siliceous pigment is present in amounts of between about 5 and about 100 parts per 100 parts by weight of rubber and the aromatic hydroxy compound, methylene donor compound and compound containing reactive amino groups are each individually present between about 0.5 and about 8 parts per 100 parts by weight of rubber.
 6. An abrasion-resistant vulcanizate of rubber selected from styrene-butadiene rubber, butadiene rubber, EPDM rubber, and natural rubber, precipitated siliceous pigment, polyethylenimine having at least five reactive amino groups, at least one of which amino groups is a primary amino group, resorcinol, and hexamethylenetetramine, wherein the siliceous pigment is present in an amount between about 5 to about 100 parts and the polyethylene imine, resorcinol and hexamethylenetetramine are each individually present in an amount between about 0.5 and about 8 parts per hundred parts by weight of rubber.
 7. The vulcanizate of claim 6 wherein the rubber is natural rubber.
 8. The vulcanizate of claim 3 wherein the polyethylenimine has at least five reactive amino groups. 